Patent GB-823218-A (GB)
Title: Improvements in or relating to position-selecting, scanning and like systems
Inventor: ARCHER JOHN
IPC: H01J29/46
Filed: 1954-12-23
Abstract: 823,218. Discharge apparatus. PHILIPS ELECTRICAL INDUSTRIES Ltd. Dec. 6, 1955 [Dec. 23, 1954], No. 34964/55. Divided out of 823,201. Class 39(1). [Also in Group XL(b)] The node X of a standing wave established on an electrically conductive double line La, Lb, Fig. 13, is employed to select a position along a half wavelength section AZ of the line. The position selected may be varied either by changing the frequency of the oscillator O feeding the line, or by varying in a complementary manner, so as to keep the total length constant, the lengths of line preceding and following section AZ. The invention is stated to be of use generally where it is desired to select from a plurality of positions or elements, such as in information storage devices of switching systems, but is described in detail only as applied to a cathode-ray display tube for use in television where the position of a luminous element on a screen is selected. The tube is constructed as shown in Fig. 18 with a planar cathode K comprising a plurality of filaments fed in parallel, an anode An in the form of a mesh of thin wires or a transparent conductive coating carrying a phosphor Ph, and a pair of grid assemblies g1, g2 disposed at right-angles to each other and each comprising strips of sheet metal perforated at regular intervals to permit passage of cathode-anode current. The ends of the strips are brought out to double lines L1a, Lib and L2a, L2b and are bonded to the respective upper conductors of the lines with the interposition of strips RC1, RC2 of imperfect insulating material. In operation, standing waves are established on the two lines and, except at the position of the nodes, cause current to be drawn from each grid strip. In effect, each grid functions as a diode, and due to the CR couplings provided between the lines and strips by the insulating strips RC1, RC2, the strips require a negative cut-off bias. The sharpness of a node may be such as to embrace only a single grid strip. As a consequence, only a single strip in each grid assembly, as determined by the positions of the nodes, will be above cut-off level allowing cathode-anode current to flow and luminance to be produced only at the intersection of the two strips. Modulation of the intensity of the luminance may be effected by signal applied either to the cathode or a grid assembly located between grid g2 and the anode. The ends of the grid strips opposite to the lines may be extended to provide marginal zones exposed to the cathode. The extensions then function to provide the diode action referred to above. This is particularly necessary in the case of grid g2 whose current is restricted by grid g1. If this feature is adopted, it is necessary, where cathode modulation is to be employed, to provide separate cathode filaments for the marginal zones insulated from the remainder of the cathode. Reference is made to the use of a pair of spaced wires connected together in place of each grid strip, and an arrangement in which only one grid is controlled by a line carrying a standing wave, the other being controlled by a switching device. The sharpness of the nodes may be improved by superimposing on the line standing waves at a higher harmonic frequency.